Study On Interfacial Interaction Mechanism Of The Effect Of Surface Morphology On Membrane Fouling In MBR

Membrane bioreactor(MBR)is a new wastewater treatment and recycling technology which incorporates membrane separation and bioprocessing technologies and the distinct advantages over traditional wastewater treatment processes.However,its wide-spread applications and promotion were significantly baffled by the membrane fouling problem.In general,membrane fouling occurs as a result of adhesion/deposition of various foulants on surface of membrane.Meanwhile,short-ranged interaction energies between membrane surface and foulants are considered as control forces determining the deposition/adhesion process.Moreover,surface morphology is one of the most important properties of membranes and their associated foulants in MBR.Meanwhile,surface morphology should take key roles in interaction energies between foulants and membrane surface.Herein,this study is to explore the interfacial interaction mechanism of the effect of surface morphology on membrane fouling by thermodynamic method.Based on the rough characteristics in nature of foulant particle and membrane surface in a MBR,regularly rough particle and membrane surfaces were constructed by using a sinusoidal sphere function and a sinusoidal membrane function,respectively.Thereafter,the novel methods,which combined XDLVO theory,surface element integration(SEI)method,composite Simpson's rule and differential geometry,were developed to quantify the interfacial interactions between the regularly rough particles or their interfacial interactions with membrane surface.The novel method in interaction calculation was verified to be correct and feasible.Moreover,the new methods were used to quantify the interfacial interaction between regularly rough surfaces and analyze the influence of the rough surface roughness parameters on the interfacial interaction and membrane fouling.The results show that there is no change in the direction of XDLVO interactions between the rough surfaces,but rough surface corresponds to much lower interaction forces than smooth surface by DA method.Meanwhile,it is also found that increase in the scaled amplitude of regularly rough particle surface and regularly rough membrane surface significantly reduced the attractive total interaction energies.The total interfacial interaction shows an unimodal pattern with the increase in surface period of rough surface.With decrease of frequency of the ripples and the increase of particle radius in the interaction scenarios of two regularly rough particles,attractive forces between two particles gradually strengthened.These confirmed that surface morphology can significantly affect the interfacial interactions between rough surfaces and the adhesion behavior of foulant particles on the membrane surface.In addition,the application prospect of the new methods in membrane fouling and interface behavior was also discussed.Further analysis of the surface morphology of membrane and foulant particle by AFM and SEM revealed that the surfaces of membrane and foulant particle were disordered and randomly rough with typical fractal characteristics.Surface morphologies of membrane and foulant particle were simulated by fractal theory represented by the modified Weierstrass-Mandelbrot(WM)function.Fractal parameters of foulant particle and membrane surface was determined by the light scattering method and the power spectrum method,respectively.Thereafter,by comparison,it was found that the reconstructed membrane and foulant particle surfaces are very close to the real surfaces.Meanwhile,the interaction scenarios of a randomly rough particle and a randomly rough membrane surface was simulated.A new method suitable for quantifying the interaction of this scenarios was proposed relying on XDLVO approach,SEI method,composite Simpson's rule and differential geometry.Based on the new method,the interaction energies between a randomly rough particle and a randomly rough membrane surface was quantified and the effect of Df on membrane fouling was investigated.It is found that Df is an important parameter affecting the surface morphology of the membrane.With the increase of Df,the surface roughness of the membrane will be significantly reduced.At the same time,with the decrease of Df,the total interaction energies between the foulant particle and the membrane will be significantly enhanced,and the foulant particle is easier to adhere to the membrane surface.Moreover,it was found that,dispersed foulants like SMPs have extremely higher fouling propensity than sludge flocs and other particulates to adhere to membrane surface.Meanwhile,the effect of surface morphology on the interfacial interaction between different types of foulants and membrane is discrepant.A more rough surface morphology,the more conducive to the adhesion of dispersed foulants(SMPs)on the membrane surface.